A complete functional nicotinic acetylcholine receptor (AChR) consisted of five subunits of four different types arranged as alpha2, beta, gamma and delta. Each of the four subunits is coded by a separate and discrete mRNA. Thus, the synthesis of a complete functional AChR molecule involves complex processes including assembly of the four different types of subunits in a particular order. The mechanisms involved in a multi-subunit AChR assembly will be studied by expressing normal, and site directed mutant, AChR subunits from cloned cDNAs in various combinations in the large oocyte cells of the frog. Specific topics to be investigated include: (1) The requirement of post-translational modifications for assembly and membrane insertion. (2) The order in which different subunits are put together. (3) Identification and localization of incomplete AChR molecules in the surface membrane. (4) The intracellular compartments in which AChR assembly occurs. (5) The presence of signals on the AChR subunits required for assembly. This research should substantially improve our understanding of the mechanisms involved in the assembly and membrane insertion of the nicotinic AChR in particular and of multi-subunit membrane proteins in general.